In 1978, most Topps baseball cards had an at-bat result on the back, like Fly Out, Double, or Ground Out. These were to be used in a two-player game. A few of the cards had the complete rules on them. Players would take turns playing three-out innings, pulling cards from the top of a deck and scoring runs (if any) until three outs were drawn, at which point the turn would pass to the other player. The game would be played to nine innings, with extra innings in the case of ties. - BoardGameGeek